JPH10221434A - Passive sonar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a noise easily and optimally by rotating a directional pattern in a direction where the S/N ratio of a target signal is maximized and receiving a sound wave. SOLUTION: A noise level measurement part 1 measures a noise level by rotating a directional pattern based on an acoustic signal that is obtained after a wave reception part 4 receives it. A signal level calculation part 2 calculates the azimuth characteristics of the signal level of a target. An azimuth calculation means 3 calculates an S/N ratio from a noise level from the noise level measurement part 1 and a signal level from the signal level calculation part 2 and outputs the maximum S/N ratio. A directivity formation part 5 rotates the directional pattern to the azimuth based on the maximum S/N ratio from the azimuth calculation part 3 and outputs an acoustic signal from the wave reception part 4 to a frequency analysis part 6 as an acoustic signal obtained in that directional pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive sonar device, and more particularly to a passive sonar device for removing noise when a target is detected by underwater acoustics using a sonobuoy.

[0002]

2. Description of the Related Art Conventionally, in a passive sonar device for detecting a target by using underwater sound using a sonobuoy, noise removal is conventionally performed when the S / N ratio is deteriorated due to the presence of a ship and it is difficult to detect an acoustic signal generated from the target. Improved detection (SN
Ratio improvement).

FIG. 6 is a block diagram of an example of a conventional passive sonar device, and FIG. 7 is a pattern diagram of each receiver in FIG. 6 and directivity in a process of forming directivity. In FIG. 6, the wave receiving unit 4 includes three kinds of wave receivers 41, 42, and 43, receives an underwater sound wave, performs acoustic-electric conversion, and outputs an acoustic signal as an electric signal. Three types of receivers 41, 42 and 4
3, the receiver 41 has a non-directional directivity as shown in FIG. 7 (A), and the receiver 42 has a directivity represented by cos θ as shown in FIG. 7 (B). And the receiver 43 is shown in FIG.
It has directivity represented by sin θ as shown in FIG.

[0006] The directivity forming section 5 shown in FIG. 6 receives an acoustic signal from the wave receiving section 4 as an input signal, and based on the azimuth α input by the operator, a null direction of the directivity (direction with the lowest sensitivity).
The directional pattern is formed using the input acoustic signal so that the direction becomes the azimuth α, and the acoustic signal obtained with the formed directivity is output to the frequency analysis unit 6. The frequency analysis unit 6 analyzes the frequency of the input acoustic signal.

Next, the operation of the conventional passive sonar device will be described. In the wave receiving section 4, the wave receivers 41, 4
In each of 2 and 43, the sound wave in water is converted into an acoustic signal, which is an electric signal, using a piezoelectric element (an element that converts a change in pressure into an electric signal), and is input to the directivity forming unit 5.

The operator uses the direction, distance, and noise radiation level of the cruise ship, which is the noise source of the sound signal of the target target, as the data, and analyzes the drawing and the like to optimally remove noise. Find the possible null direction bearing.
Here, the “azimuth” is an azimuth using the position of the wave receiving unit 4 as a reference point. Normally, when there is only one ship, the null direction is set as the direction of the ship. This is because, since the receiving sensitivity in the null direction is low, the direction of the null direction is directed to the cruise ship, so that the noise of the cruise ship can be reliably removed. The azimuth in the null direction obtained by the analysis is input to the directivity forming unit 5 as the azimuth α.

The directivity forming unit 5 multiplies the acoustic signal input from the receiver 42 by cos α by the multiplier 51 and the acoustic signal input from the receiver 43 to the multiplier 5.
The result obtained by multiplying sinα by 2 is added by the adder 53. The directivity at this time is expressed as in equation (1), and the directivity pattern is as shown in FIG.

Cos θ · cos α + sin θ · sin α = cos (θ−α) (1) That is, the acoustic signals obtained by the two receivers 42 and 43 are multiplied and added, so that co is rotated by α.
It is the same as the acoustic signal obtained by the receiver having the directivity pattern of sθ.

Further, the directivity forming section 5 multiplies the addition result obtained by the adder 53 by “−1” by the multiplier 54 and supplies the result to the adder 55, where the sound from the receiver 41 is reproduced. Add to signal. The directional wave at this time is expressed as in equation (2), and the directional pattern is as shown in FIG.

1-cos (θ-α) (2) The directivity pattern shown in FIG.
ARDIOID).

In the directivity forming section 5, by changing the input direction α from the output acoustic signals of the three receivers 41, 42 and 43 of the receiving section 4, the directivity pattern can be arbitrarily rotated. A possible cardioid directivity can be obtained. The acoustic signal obtained by the directivity formed by the directivity forming unit 5 is supplied to the frequency analyzing unit 6 and subjected to frequency analysis.

As described above, by changing the value of the azimuth α, it is possible to rotate the directivity pattern, to receive the noise of the cruise ship at a low receiving sensitivity, and to receive the target signal. Reception is performed at high sensitivity to reduce the reception level of the noise of the cruise ship and remove noise. In the conventional apparatus, the noise removal processing increases the SN ratio of the target signal, thereby improving detection.

Further, as another conventional sonar device, in order to remove noise, noise is received by a receiver having low reception sensitivity in a target direction, and noise obtained by a main receiver is obtained. There is known a sonar device that performs weighting according to the degree of correlation with the noise and removes noise having a high degree of correlation (Japanese Unexamined Patent Publication No. Hei.
275379).

[0014]

However, in the conventional passive sonar device shown in FIG. 6, the position (distance) of a cruise ship, the radiation level of noise, and the position of a receiver are required for optimal noise removal. However, in practice, it is difficult to obtain such information accurately. It may not be possible.

Further, when there are a plurality of ships, the experience and information of the operator are required, and the operator comprehensively analyzes while drawing, etc., and obtains the azimuth in the null direction. There is also a problem that a long time is required for the process of obtaining the azimuth in the null direction.

In the sonar device described in Japanese Patent Application Laid-Open No. 2-275379, there is no description of a technique for measuring noise directional characteristics, calculating an SN ratio, and removing noise.

The present invention has been made in view of the above points,
It is an object of the present invention to provide a passive sonar device that can easily and optimally remove noise.

Another object of the present invention is to provide a passive sonar device which can obtain a null direction azimuth capable of optimally removing noise in a short time.

[0019]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a wave receiving section comprising a plurality of wave receivers having different directivities and receiving sound waves and converting them into acoustic signals. Receiving the acoustic signal from the receiving unit as an input signal,
A noise level measurement unit that measures a noise level by rotating a directional pattern, and a reception level of a signal that would be obtained when the directional pattern is rotated, assuming that a target exists in a target azimuth. The signal level calculation unit to calculate, and the noise level measured by the noise level measurement unit,
An azimuth calculator for calculating the SN ratio of each azimuth by dividing the reception level calculated by the signal level calculator, and calculating the azimuth indicating the maximum SN ratio among the azimuths, and a maximum SN ratio calculated by the azimuth calculator And a directivity forming unit that forms a directivity pattern based on the azimuth and outputs an acoustic signal from the wave receiving unit as an acoustic signal obtained by the directivity pattern.

According to the present invention, the directivity pattern is rotated, the noise level and the reception level are calculated, and based on these, the directivity pattern is formed based on the azimuth indicating the maximum SN ratio. Since the audio signal is output as an audio signal obtained by the formed directivity pattern, once the target target azimuth is set, the audio signal can be received in the directivity pattern that always provides the maximum SN ratio.

Further, the present invention receives a target target frequency and an acoustic signal from a receiving unit as input signals, and determines the direction of arrival of the target target frequency acoustic signal based on the level ratio and phase of the input acoustic signal. A difer processing unit is further provided for analyzing and inputting the analyzed azimuth as a target azimuth to a signal level calculation unit.

According to the present invention, when the frequency of the target is set, the direction of the target can be tracked even if the target moves, so that the null direction can be analyzed by performing a drawing or the like based on the experience and information of the operator. The conventional operation of finding the azimuth is not required, and the operator can automatically set the optimal directional pattern direction only by inputting the target frequency.

[0023]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of a first embodiment of the passive sonar device according to the present invention. In FIG.
The same components as those described above are denoted by the same reference numerals. The embodiment shown in FIG. 1 has a configuration of a conventional passive sonar device,
This is a configuration in which a noise level measuring unit 1, a signal level calculating unit 2, and an azimuth calculating unit 3 are added.

In FIG. 1, the receiving unit 4 comprises a non-directional receiver 41, a receiver 42 having a directivity of cos θ, and a receiver 43 having a directivity of sin θ. The signal is received, and is subjected to acoustic-electrical conversion to generate an acoustic signal, which is output to the noise level measuring unit 1 and the directivity forming unit 5, respectively. In FIG. 1, for example, a wave receiving unit 4 is installed in the sea as a sonobuoy, and the obtained acoustic signal is wirelessly transmitted, and a noise level measuring unit 1, a signal level calculating unit 2,
For example, an aircraft equipped with the azimuth calculation unit 3, the directivity forming unit 5, and the frequency analysis unit 6 receives this.

The noise level measuring unit 1 receives the acoustic signal from the wave receiving unit 4, forms a directivity pattern, and measures (actually measures) the azimuth characteristics of the received noise level. Here, the “azimuth characteristic” is a characteristic obtained when the azimuth is changed from 0 to 360 degrees based on the null direction (minimum sensitivity) of the directivity pattern. The signal level calculator 2
Assuming that the target of interest is in the azimuth β, the azimuth characteristic of the received signal level is calculated.

The azimuth calculation unit 3 calculates the noise level L _N (α) measured by the noise level measurement unit 1 and the signal level calculation unit 2
The direction characteristic L _S (α, β) calculated in step (1) is received as an input signal, the direction characteristic of the SN ratio is calculated, and the direction αβ with the maximum SN ratio is sent to the directivity forming unit 5. Directivity forming unit 5
Rotates the directivity pattern based on the input azimuth αβ that is the maximum SN ratio, and uses the acoustic signal from the wave receiving unit 4 to convert the acoustic signal obtained by the rotated directivity pattern into the frequency analysis unit 6. To supply. The frequency analysis unit 6 performs a frequency analysis on the input acoustic signal.

Next, the operation of the first embodiment will be described with reference to FIGS. 2, 3 and 4. The sound waves emitted from the target target, the ship and the like, propagate in the water, reach the receivers 41, 42, and 43 in the receiver 4, and are converted into acoustic signals, which are electric signals, respectively. . The acoustic signals extracted from the receivers 41, 42, and 43 are supplied to the noise level measuring unit 1 and the directivity forming unit 5, respectively.

First, the noise level measuring section 1 temporarily stores the acoustic signal input from the wave receiving section 4. The reason why the acoustic signal is temporarily stored is that the same acoustic signal is used for measurement in all directions to accurately measure the directional characteristics of the noise level. Next, the noise level measuring unit 1
FIG. 2 (A) uses this temporarily stored acoustic signal.
The noise level is measured according to the flow chart of FIG.

That is, the noise level measuring section 1 first
The null direction α is set to 0 ° (step 101), a directivity pattern in this case is formed (step 102), and the noise level obtained by this directivity pattern is measured (step 103). Here, the measurement of the noise level is an average of several measurement values. This is because the noise level in the real environment is likely to fluctuate and stable measurement is performed. The directivity pattern is formed by the same method as the directivity forming section 5 of the conventional passive sonar device shown in FIG.

Next, the noise level measuring section 1 calculates the measured noise level data L _N (α) (here, α = 0
Is sent to the direction calculation unit 3 (step 10).
4). Subsequently, the value of the azimuth α is shifted by a certain angle d (step 105), and it is determined whether or not the azimuth α is equal to or more than 360 ° (step 106). In the same manner, a directivity pattern in the case of .degree. Is formed (step 102), the noise level is measured (step 103), and the noise level data L
_N (α) is transmitted (step 104).

Here, the value of the angle d of the shift amount of the azimuth α is optimally the same as the azimuth accuracy desired by the operator. For example, if the operator wants to obtain the noise level with an accuracy of 10 °, the angle d is 10 °
And In this noise measurement process, the null direction azimuth α is sequentially increased by an angle d, and the measurement and transmission of the noise level in each direction are performed.
It repeats within the range of ° (steps 102 to 106).

As a reference, as shown in FIG. 3, the wave receiving section 4 (Sonobuoy) of the passive sonar device is located at the position indicated by 20, and the ships a and b are arranged with respect to the wave receiving section 4 (20). It is assumed that the target target 30 exists in the azimuth rotated by 70 ° and 310 ° clockwise from the north direction, and that the target 30 exists in the azimuth rotated 170 ° (= β) clockwise from the north direction. In this case, the azimuth characteristic of the noise level as shown in FIG. 4A can be obtained by measurement. Here, since the null direction (the direction with the lowest sensitivity) is used as a reference, it can be seen that the noise level is the lowest between the cruise ships a and b (azimuth 30 °).

On the other hand, the signal level calculator 2 shown in FIG.
Is based on the target target azimuth β input from the operator, and assuming that the target exists in the azimuth β, the reception level of the signal that would be obtained when the directivity pattern was rotated is shown in FIG. ) Are calculated according to the flowchart shown in FIG.

That is, the signal level calculator 2 firstly
The azimuth α in the null direction is set to 0 ° (step 201), and the signal level L that will be obtained by the directivity pattern in this case is set.
_S (α, β) is calculated based on the following equation (Step 20)
2).

L _S (α, β) = 1−cos (β−α) (3) Therefore, the signal level L _S when the azimuth α = 0 in the null direction
(0, β) is obtained from equation (4) by substituting α = 0 into equation (3).

L _S (0, β) = 1−cos (β−0) (4) The signal level calculator 2 calculates the direction of the data of the signal level L _S (0, β) calculated by the equation (4). After output to the unit 3 (step 203), the value of the azimuth α is shifted by a certain angle d (step 204), and the azimuth α after the shift is 360
(Step 205), and
When it is less than 0 °, the processing of steps 202 to 204 is executed again. Hereinafter, in the same manner as described above, the signal level calculator 2 sequentially increases the null direction azimuth α by the angle d, and obtains the signal level of the signal level that would be obtained in a directivity pattern in which each direction is the null direction. The calculation and the transmission of the calculation result are repeated when the azimuth α in the null direction is in the range of 0 to 360 °.

Therefore, as shown in FIG. 3, the signal level calculator 2 determines that the target 30 is 1 clockwise from the north direction.
If it exists in the azimuth rotated by 70 ° (= β), the azimuth characteristic of the signal level as shown in FIG. 4B is obtained by substituting 170 ° into β in equation (3). In FIG. 4B, when the null direction is directed to the azimuth of 170 °, that is, the direction of the target 30, the signal of the target 30 is not received.

The azimuth calculation unit 3 shown in FIG. 1 receives the above-mentioned noise level L _N (α) and signal level L _S (α, β) as input signals, and according to the flowchart shown in FIG. Perform calculations. That is, the azimuth calculation unit 3 firstly
The directional α in the null direction is set to 0 ° (step 301), and the S / N ratio S / N that would be obtained by the directivity pattern in this case
(Α, β) is calculated based on the following equation (step 30).
2).

S / N (α, β) = L _S (α, β) L _N (α) (5) Accordingly, S / N (0,
β) is obtained by substituting α = 0 into the equation (5).
Obtained from the equation.

S / N (0, β) = L _S (0, β) L _N (0) (6) The azimuth calculation unit 3 calculates the S / N (0, β) calculated by the equation (6).
After the data of β) is temporarily stored, the value of the azimuth α is shifted by a certain angle d (step 303), and it is determined whether or not the azimuth α after the shift is 360 ° or more (step 3).
04) If it is less than 360 °, step 302 is performed again.
And 303 are executed.

Thereafter, in the same manner as described above, the azimuth calculation unit 3
Calculates the S / N ratio that would be obtained in a directivity pattern in which each direction is a null direction, by sequentially increasing the null direction azimuth α by an angle d, and calculates the null direction azimuth α from 0 to 360 °. Repeat in the range. Accordingly, when the cruise ships a and b and the target 30 are present at the positions shown in FIG. 3, the azimuth calculation unit 2 obtains the results shown in FIGS. 4A and 4B from the results shown in FIGS. The azimuth characteristics as shown in ()) are obtained.

Subsequently, the azimuth calculation unit 2 searches the azimuth αβ at which the SN ratio becomes maximum from the calculated azimuth characteristics (step 305). The azimuth αβ at which the SN ratio is the maximum is the null azimuth from which noise can be optimally removed. The reason is that the maximum SN ratio means that the ratio of the signal level to the noise level is the maximum. If the directional pattern is rotated in the direction of the azimuth αβ at which the SN ratio becomes the maximum, an acoustic signal can be obtained. , Noise is reduced. The azimuth αβ at which the obtained SN ratio becomes the maximum
Is sent to the directivity forming unit 5 in FIG. 1 (step 30).
6).

The directivity forming unit 5 forms a directivity pattern having the null direction as the direction αβ based on the direction αβ at which the input SN ratio becomes the maximum, and frequency-analyzes the acoustic signal obtained by the direction pattern. Output to the unit 6. Frequency analysis unit 6
Analyzes the frequency of the input acoustic signal. Further, since the ship-going ship and the like move with the passage of time and the state of the noise level changes, the entire process is repeated at regular intervals.

As described above, even if a plurality of hulls and ships are present by rotating the directivity pattern and obtaining an acoustic signal, the noise of the hulls and hulls is generally received at a low level and the signal of the target target is received at a high level. can do.

According to the first embodiment, noise reduction while waiting in a fixed direction can be realized. The reason is that once the azimuth of the target target is set, the optimum noise removal can always be performed even if the cruise ship moves and the situation of the noise level changes. This is a noise reduction method that is effective when the direction of existence of the target target is determined or estimated in the operation of target detection.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows a block diagram of a second embodiment of the passive sonar device according to the present invention. In the figure, the same components as those in FIG.
The description is omitted. As shown in FIG. 5, in the second embodiment, a difer (DIFER: directional fr) for analyzing a direction of arrival of a signal is provided between a receiving unit 4 and a signal level calculating unit 2.
It is characterized in that a processing unit 7 is provided.

The difer processing unit 7 analyzes the direction of arrival of the sound signal for each frequency from the level ratio and phase of the sound signals sent from the three receivers 41, 42 and 43 constituting the wave receiving unit 4. And a processing unit for outputting. When the operator inputs the target frequency to the difer processing unit 7, the difer processing unit 7 analyzes the direction of arrival of the signal of the input frequency, and sends the azimuth β to the signal level calculation unit 2 instead of the operator of the first embodiment. Enter The later operation is the first
The operation is the same as that of the embodiment.

The effect of the second embodiment is that noise can be reduced by waiting at a constant frequency, in comparison with the effect of the first embodiment (standby in a fixed direction). The reason is that once the frequency is set, even if the target target moves, the direction of the target target is tracked by the difer processing unit 7, and optimal noise removal can always be performed. this is,
In the operation of target detection, this method is an effective noise reduction method when a target is determined (generation frequency is known) and the target moves.

[0050]

As described above, according to the present invention,
Since the directivity pattern is rotated in a direction in which the S / N ratio of the target signal is maximized to receive sound waves, noise can be reduced optimally.

Further, according to the present invention, the operator sets the direction of the directivity pattern that enables optimal noise removal by simply inputting the target direction or frequency.
Operator load can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of each unit in FIG. 1;

FIG. 3 is a diagram showing a relationship between a ship and a target target position to which the present invention is applied.

FIG. 4 is a diagram showing azimuth characteristics obtained by the apparatus of the present invention shown in FIG. 1 in the case of FIG. 3;

FIG. 5 is a block diagram of a second embodiment of the present invention.

FIG. 6 is a block diagram of a conventional example.

FIG. 7 is a pattern diagram of each receiver in FIG. 6 and directivity in a process of forming directivity.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 noise level measurement unit 2 signal level calculation unit 3 azimuth calculation unit 4 reception unit 5 directivity formation unit 6 frequency analysis unit 7 difer processing unit 41, 42, 43 receiver 51, 52, 54 multiplier 53, 55 addition vessel

Claims (3)

[Claims] 1. A receiving unit comprising a plurality of receivers having different directivities and receiving sound waves and converting them into acoustic signals, respectively, and receiving the acoustic signal from the receiving unit as an input signal. ,
A noise level measurement unit that measures a noise level by rotating a directivity pattern, and a reception level of a signal that would be obtained when the directivity pattern is rotated, assuming that a target exists in a target target direction. A signal level calculation unit to calculate, and a noise level measured by the noise level measurement unit,
An azimuth calculation unit that calculates the S / N ratio of each azimuth by dividing the reception level calculated by the signal level calculation unit, and calculates the azimuth that indicates the maximum S / N ratio from among them, and the maximum calculated by the azimuth calculation unit. A directivity forming section that forms a directivity pattern based on the azimuth indicating the SN ratio, and outputs an acoustic signal from the wave receiving section as an acoustic signal obtained by the formed directivity pattern. Passive sonar device. 2. A target target frequency and an acoustic signal from the wave receiving unit are received as input signals, and an azimuth of arrival of the target target frequency acoustic signal is analyzed from a level ratio and a phase of the input acoustic signal. 2. The passive sonar device according to claim 1, further comprising a difer processing unit for inputting the analyzed direction as the target target direction to the signal level calculation unit. 3. The receiver comprises a first receiver having no directivity, a second receiver having directivity of cos θ, and a third receiver having directivity of sin θ. The noise level measuring unit measures the noise level L _N (α) in each of the directivity patterns in which the null direction azimuth α is shifted by a certain angle in the range of 0 ° to 360 °, and The calculation unit calculates 0 ° to 3 ° based on the target target direction β.
The signal level L _S (α, β) in each of the directivity patterns in which the azimuth α in the null direction is shifted by a constant angle in the range of 60 ° is calculated by {1-cos (β-α)}. The azimuth calculation unit calculates a calculation formula L _S (α, α, に お い て) for each of the directivity patterns in which the azimuth α in the null direction is shifted by a certain angle in the range of 0 ° to 360 °.
β) / L _N (α), the maximum orientation α
3. The passive sonar device according to claim 1, wherein β is determined.